The present invention relates to an improvement of a thermal head, in particular, relates to a thermal head with an improved protection layer which covers a heater layer.
The present thermal head is used not only for a thermal printer, but also a thermal ink transfer printer.
A thermal head has at least a substrate, a heater layer deposited on the substrate together with a conductive lead layer for feeding to said heater layer, and a protection layer covering said heater layer.
Conventionally, a protection layer is deposited on a heater layer through sputtering process, or thick film process for the purpose of preventing oxidization and wearing of a heater layer. Said protection layer is conventionally made of T.sub.a2 O.sub.5, S.sub.i O.sub.2, or glass.
However, an evaporation process, and/or sputtering process has the disadvantage that the cost of the same is high, although it provides an excellent protection layer. Further, if conventional protection layer is made through a thick film process, it must be fired at high temperature, for instance about 1000.degree. C. When a substrate is made of ceramics, that fired protection layer is available. However, when a substrate is made of plastics, for instance, polyimide film, a fired protection layer is not suitable, since a polyimide film is not heat-proof and unstable at high temperature.
Since a thermal head with a substrate made of ceramics is high in cost, it has been desired to use a polyimide film as a substrate of a thermal head. Although plastics, like polyimide resin, can be coated on a heater layer at low temperature, it is not wear-proof. Therefore, a protection layer which can be coated on a polyimide film with low temperature, and having wear-proof characteristics has been desired.